1. Field of the Invention
The present invention relates to an inkjet recording device that reliably and rapidly prints high-quality images and includes a recording head and a cleaning device for cleaning the recording head.
2. Related Art
A line-scan inkjet recording device has been known for printing images on a continuous recording sheet at high speeds. The line-scan inkjet recording device includes an inkjet recording head that extends across the entire width of the continuous recording sheet. The inkjet recording head is formed with a row of orifices through which ink droplets are ejected. The recording head is aligned in confrontation with a surface of the recording sheet. The recording sheet is transported in a main scan direction rapidly while the recording head is ejecting ink droplets from selective ones of the orifices in accordance with a recording signal. By transporting the recording sheet in the main scan direction while ejecting ink in this manner, recording dots can be selectively formed in scan lines on the recording sheet to produce a desired recording image.
There have been proposed various types of line-scan inkjet recording devices, such as devices that use a continuous inkjet type recording head and devices that use a drop-on-demand type recording head. Although drop-on-demand inkjet type line-scan inkjet recording devices have a slower printing speed than do continuous inkjet type devices, they have an extremely simple ink system and so are well suited for a general-purpose high-speed recording device.
Japanese Patent-Application Publication No. 2001-47622 discloses a drop-on-demand line-scan inkjet recording head that includes a plurality of head modules aligned across the width of the recording sheet. Each head module is formed with a nozzle row that includes a plurality of nozzle orifices. The nozzle rows are slanted at an angle with respect to a sheet feed direction. By using the plurality of head modules, the nozzle pitch in the widthwise direction of the recording sheet can be set quite small, so that high resolution images can be formed.
Some nozzles of the drop-on-demand line-scan inkjet recording head will not be fired for long periods of time because ink droplets are only ejected as needed to form recording dots in accordance with recording data. If nozzles are not fired for long periods of time, then ink near the nozzle orifice can dry. This unstabilizes ink ejection performance. In order to overcome this problem, the present applicant has proposed to dispose a charge deflecting electrode on the surface of each head module in U.S. patent application Ser. No. 10/363,822, now U.S. Pat. No. 6,796,632 to Yamada et al. issued Sep. 28, 2004. Each charge deflecting electrode is oriented parallel with the corresponding nozzle row and includes an ink receiving portion. The charge deflecting electrodes generate a slanted electric field that deflects ink droplets from the nozzle orifices to impinge on a desired location of the recording sheet. The slanted electric field also deflects refresh ink droplets from the nozzle orifices to U-turn away from the recording sheet and impinge on the ink receiving portion, where the ink is collected. By selectively ejecting refresh ink droplets in this manner, the problem of ink near the nozzle orifices becoming excessively viscous can be prevented so that ink ejection can be maintained stable.
Usually, a drop-on-demand inkjet recording head needs to be cleaned using a recording head cleaning device in order to maintain stabilized ink ejection. The recording head cleaning device removes viscous ink, deteriorated ink, or foreign matters, such as paper dust, that clings to the nozzle orifices. A purge unit is an example of such a recording head cleaning device. A purge unit performs a purge operation and a wiper operation. During purge operations, a cap is brought into intimate contact with one or more nozzle orifices, and ink is sucked from the nozzle orifices through the cap. The wiper operation is performed after the purge operation. During the wiper operation, a rubber blade is driven to slide across the area surrounding the nozzle orifices to wipe off the area and restore the ink meniscus to a proper condition. Japanese Patent-Application Publication No. 2001-260392 proposes a cleaning device that brings a suction hole of a suction nozzle into confrontation with, but not in contact with, a portion of the nozzle orifices. A negative pressure is developed in the suction hole while the suction nozzle is moved along the row of the nozzle orifices to clean the nozzle orifices.
However, the above-described purge unit cannot be easily used for the recording head described in U.S. Pat. No. 6,796,632. That is, the surface of the charge deflecting electrode is higher than the nozzle surface, so there is a level difference between the nozzle surface and the charge deflecting electrode that follows the nozzle orifice rows. This level difference makes difficult to side the blade around the nozzle orifices to restore the meniscus in the nozzle orifices.
The cleaning device disclosed in Japanese Patent-Application Publication No. 2001-260392 does not take the charge deflection electrode into consideration and so does not sufficiently clean areas around the nozzle orifices and the edge portion of the charge electrode. Foreign matter, such as paper dust and deteriorated ink, is easily caught in spaces where the ink receiving portion and the charge deflecting electrode connect, on burs produced when the charge deflecting electrode is cut, and in unevenness in the surface of the ink receiving portion. It has been difficult to properly removes foreign matter that clings in such areas.